timer with LED 4 digit display

Hi, I need some help to build up a timer with 2 display with 4 digit each, based on arduino. Has to start when a contact is closed ( a micro switch with contact N.O. is closing for a short time, giving a short impuls) and then to display the time (minute and seconds). After the set time is end, the display to be reset and wait for another cycle thanks

Use a max7219 to drive your two displays. That will make whole circuit much easier. Choose common cathode displays for use with max7219, with a segment voltage of less than 5V.

When you say that the display should show "minutes and seconds" is that elapsed time or real time? What is the other display for? It would help if you explained what the purpose of your circuit is.

Hi, we are building self service car wash units, and for this purpouse I need this timer. One display id for the client (only display) and the other one is placed in the technical chamber (were are all the pumps and motors and electrical devices) So when a client cames to wash his car, he buy a token, introduce it into a token reader, and automatically is activated the washing bay. So the timer will show the elaspsed time up to the set time (for example: 4 minutes and 30 seconds; show as 04:30) In this period the client can choose any available program, foam, wax, high pressure rinsing.... This timer should be able also to count how many token was used.

In this kind of application I saw different kind of PLC, but is seem to be so complicated, what I need is something simple and efficient Thanks

How large must these displays be? My suggestion of max 7219 may not be the best or easiest for large displays with segment voltage more than 5V.

If they are quite small and less than 5V, it might be better to have a separate max7219 chip for each display, to keep the wiring simple.

I will like to have a WENRUN LFD080AAG-103-01 Display: LED; 7-segment; 20.32mm; green; 5.6mcd; cathode; No.char:4 I think I'ts OK and can be used Thanks

Yes, those displays will be fine to use with max 7219. Here is the data sheet. Under "maximum ratings" it says the forward current is 20mA continuous and 80mA peak. Under "electrical characteristics" it says the forward voltage is between 2.0 and 2.5V.

How far apart will the two displays be?

aprox 6 m

You have a couple of options. I'm not sure how well either will work over 6m. Experiment to find out.

  1. Run 12 cables/cores to the remote display and use a single max7219 chip. 2 x Ethernet cables would have 16 individual cores, so more than enough.

  2. Run 5 cables/cores to the remote display and have a second max7219 chip attached to the remote display. One Ethernet Ethernet cable would be enough.

Thank you